The present invention relates to a high frequency heating apparatus, and more particularly, to a microwave oven or electronic oven equipped with a rotary table or turntable for receiving thereon an object to be heated.
A microwave oven which is now widely used essentially includes an oven-defining structure preferably of double wall construction provided therein with a heating cavity or heating chamber having a hingedly supported door which is adapted to selectively open and close an access opening formed at one side of the oven defining structure, and a magnetron assembly for generating high frequency energy so as to heat an object or food material placed within the heating cavity based on the principle of dielectric heating. Some known microwave ovens are further provided with rotary tables or turntables within the heating chambers for rotation together with the objects or food material mounted thereon so that the degree of heating of such objects is made uniform by causing them to move within the heating chambers.
Conventionally, in a microwave oven equipped with a rotary table of the above described type, the rotational force of a motor employed as a driving source is mechanically transmitted via reduction gears to a rotary shaft which extends into the heating chamber through the bottom plate thereof and which is fitted, for example, into a corresponding opening formed in the rotary table, while a plurality of rollers are rotatably disposed between the lower surface of the rotary table and the bottom plate of the heating chamber for smooth rotation of the rotary table.
The conventional microwave ovens of the above described type, however, have various disadvantages in that;
(I) Since the rotary shaft extends into the heating chamber through the bottom plate thereof, excessive heat generation, electric wave leakage and the like tend to take place during operation of the microwave oven, at the area where the rotary shaft projects into the heating chamber, and for the prevention of such inconveniences, the construction of the microwave oven is undesirably complicated, with consequent high cost.
(ii) The projection of the rotary shaft into the heating cavity and the provision of the rollers undetachably disposed within the heating chamber for smooth rotation of the rotary table make it difficult to clean the interior of the heating cavity in an efficient manner.
(iii) Drops of oil, juice and the like produced by the food material during cooking in the heating chamber, or water used for cleaning the interior of the heating chamber tend to leak out of the heating chamber through the clearance between the rotary shaft and the bottom plate of the heating chamber and to pass toward the motor, reduction gears and the like, thus not only giving rise to various operational problems, but also emitting unpleasant odors over the course of time.
(iv) Since the rotary table is mechanically coupled to the rotary shaft, it is difficult to readily remove the rotary table when necessary.
(v) Although non-magnetic metallic material is most suitable for the walls of the heating chamber for various reasons, such non-magnetic metallic material is expensive, thus resulting in a high cost of the miccrowave oven. On the other hand, if less expensive magnetic metallic material is employed, corrosion of such material comes into question.
(vi) When a vessel or container of glass, ceramic material and the like, with food material placed therein, is mounted on the rotary table, such vessel of hard material tends to damage the walls of the heating chamber upon contact therebetween during rotation of the rotary table or during insertion and withdrawal of the vessel into and from the heating chamber.